1. Field of the Invention
The invention relates generally to a magnetic resolver, and more specifically, to a magnetic resolver that detects the rotational position of a rotating body.
2. Description of the Related Art
Related arts pertaining to a magnetic resolver that detects the rotational position of a rotating body using magnetic induction are described in, for example, Japanese Patent Application Publication No. 2007-171131 (JP-A-2007-171131), Japanese Patent Application Publication No. 2007-285774 (JP-A-2007-285774), and Japanese Patent Application Publication No. 2005-207748 (JP-A-2005-207748).
FIG. 9 is a cross-sectional view schematically showing the configuration of an existing magnetic resolver 101. As shown in FIG. 9, the magnetic resolver 101 includes a stator core 110, a substrate 120 on which a coil 130 is formed, and a rotor 150 that is provided so as to face the stator core 110 with the coil 130 interposed between the rotor 150 and the stator core 110. A surface of the coil 130, which faces the rotor 150, is covered with and protected by a resin cover 140.
The stator core 110 has a base plate 111 and a protrusion 112. The base plate 111 is made of iron-based magnetic material and has a ring shape. The protrusion 112 is formed integrally with the base plate 111 by machine-processing such as press working. The protrusion 112 has a side wall 114 and a ceiling 116. The side wall 114 extends upward from the base plate 111. The ceiling 116 closes an end portion of the side wall 114, which faces the rotor 150. Formed inside the protrusion 112 is a space 118 defined by the side wall 114 and the ceiling 116.
FIG. 10 is a view schematically showing flows of magnetic flux in the existing magnetic resolver 101. As shown by solid-line arrows in FIG. 10, magnetic flux generated by the coil 130 passes through the inside of the stator core 110 and is output to the rotor 150. However, as shown by broken-line arrows in FIG. 10, a portion of the magnetic flux generated by the coil 130 travels through the inside of the ceiling 116 and the space 118 but does not come out of the stator core 110. Thus, such magnetic flux is not output from the protrusion 120 of the stator core 110 toward the rotor 150.
When such magnetic flux (leakage flux) that is not output to the rotor 150 increases, the output voltage decreases, and therefore, the ratio of the output voltage to the input voltage (transformer ratio) decreases. As a result, the detection resolution of the magnetic resolver 101 deteriorates, and the rotation angle of the rotating body is not accurately detected.